1. Field of the Invention
The present invention relates generally to pharmaceutical products and methods and, more specifically, to methods for identifying compounds which can modulate the immune system, further, to methods for identifying proteins regulated by Scurfin and those that induce or inhibit Foxp3 expression.
2. Description of the Related Art
A number of autoimmune diseases, such as Inflammatory Bowel Disease, Multiple Sclerosis, rheumatoid Arthritis, and Asthma, involve immune dysregulation. In all these diseases, subsets of T cells are hyper-activated and contribute to an immune reaction towards self. In recent years, mice with mutations in CD95, CD95-ligand, CTLA-4 or TGF-β have proven useful for dissecting a number of pathways involved in T cell regulation and immune system homeostasis. Mice with mutations in any one if the above genes have profoundly altered immune responses, attributed to a failure to control T cell function.
T cell activation in the periphery involves signaling via the T cell receptor and CD28 costimulation (reviewed in Bluestone, J. A., Immunity 2:555-559 (1995); Jenkins, M. K., Immunity 1:443-448 (1994); Rudd, C. E., Immunity 4:527-534 (1996)). Down regulation of peripheral T cell responses involves several pathways. Some of these include apoptosis mediated by members of the TNFR family, including CD95 and its ligand, activation induced death due to cytokine withdrawal, and negative signaling through CTLA-4 (CD152) (Lenardo et al., Ann. Rev. Immun. 17:221-253 (1999); Oosterwegel et al., Curr. Opin. Immun. 11:294-300 (1999); Saito, T., Curr. Opin. Immun. 10:313-321 (1998); Wallach et al., Ann. Rev. Immun. 17:331-367 (1999)). Mutations or expression of dominant negative forms of some of these genes have proven their critical role in the regulation of peripheral T cell responses. Mutations in CD95, CD95L, TGF-β or CTLA-4 lead to progressive autoimmune lymphoproliferative disorders (Kulkarni et al., Proc. Nat'l. Acad. Sci. USA 90:770-774 (1993); Shull et al., Nature 359:693-699 (1992); Takahashi et al., Cell 76:969-976 (1994); Tivol et al., Immunity 3:541-547 (1995); Watanbe-Fukunaga et al., Nature 356:314-347 (1992); Waterhouse et al., Science 270:985-988 (1995)). More recent data suggests that regulation of T cell activity by CD4+CD25+ regulatory T cells is also important for maintaining peripheral T cell tolerance (Roncarolo et al., Curr. Opin. Immun. 12:676-683 (2000); Sakaguchi, S., Cell 101:455-458 (2000); Shevach, E. M., Ann. Rev. Immun. 18:423-449 (2000)). Depletion of such regulatory T cells from normal animals leads to development of various autoimmune diseases and the adoptive transfer of these regulatory cells can also prevent disease in vivo in a number of systems (Asano et al., J. Exp. Med. 184:387-396 (1996); Sakaguchi et al., J. Immun. 155:1151-1164 (1995); Suri-Payer et al., J. Immun. 160:1212-1218 (1998)).
The specific mechanism by which regulatory T cells (T-reg cells) mediate their suppressive effect is currently unclear. While TGFB and IL-10 can mediate suppressive effects, and blocking these cytokines eliminates suppression in some in vivo models, there is good evidence to indicate other molecules are also involved. Mounting evidence indicates a role for CD152 in the activation and/or function of CD4+CD25+ T cells (Read et al., J. Exp. Med. 192:295-302 (2000); Takahashi et al., J. Exp. Med. 192:303-310 (2000)). Intriguingly, several studies suggest that signaling through CD152 results in the induction of TGFB (Chen et al., J. Exp. Med. 188:1849-1857 (1998); Gomes et al., J. Immunol. 164:2001-2008 (2000); Kitani et al., J. Immunol. 165:691-702 (2000)), providing a potential link between TGFB-mediated inhibition and the inhibitory activity of CD4+CD25+ cells.
The X-linked lymphoproliferative disease observed in the scurfy (sf) mouse, a spontaneous mutant animal that shares many characteristics with the pathogenesis seen in targeted deletions of CTLA-4 (Tivol et al., Immunity 3:541-547 (1995); Waterhouse et al., Science 270:985-988 (1995)) as well as TGF-β (Kulkarni et al., Proc. Nat'l. Acad. Sci. USA 90:770-774 (1993); Shull et al., Nature 359:693-699 (1992)), including death by three weeks of age (Godfrey et al., Am. J. Pathol. 145:281-286 (1994); Godfrey et al., Proc. Nat'l. Acad. Sci. USA 88:5528-5532 (1991); Godfrey et al., Am. J. Pathol. 138:1379-1387 (1991); Kanangat et al., Eur. J. Immunol. 26:161-165 (1996); Lyon et al., Proc. Nat'l. Acad. Sci. USA 87:2433-2437 (1990)). In sf animals, disease is mediated by CD4+ T cells, and these cells exhibit an activated phenotype both in vivo and in vitro (Blair et al., J. Immunol. 153:3764-774 (1994)). The specific mutation responsible for the disease has been recently cloned and the gene shown to be a new member of the forkhead family of transcription factors (Brunkow et al., Nature Genetics 27:68-72 (2001)). The gene has been designated Foxp3 and the protein product, scurfin. Mutations in the orthologous human gene cause a similar lymphoproliferative disorder among affected male progeny, which if left untreated is generally fatal (Bennett et al., Nature Genetics 27:20-21 (2001); Chatila et al., JM2, J. Clin. Invest. 106:R75-81 (2000); Wildin et al., Nature Genetics 27:18-20 (2001)).
The present invention discloses methods and compositions useful for diagnosing scurfy-related diseases, more specifically, to methods for identifying compounds which can modulate the immune system, further, to methods for identifying proteins regulated by Scurfin and those that induce or inhibit Foxp3 expression